State Machine By Claude

Mon, 9 March 2026 | 43:30

State Machine Notes

Core Elements

Element Description
State A condition the system is in (e.g. Draft, Published)
Transition An arrow from one state to another, triggered by an event
Event What causes the transition (e.g. publish, cancel)
Guard A condition that must be true for a transition to fire (e.g. [price > 0])
Action What happens during a transition (e.g. / send_email)
Initial state Filled black circle — where the machine starts
Final state Black circle with a ring — terminal condition

Events

An event triggers a state transition. Syntax:

EventName [Guard] / Action

Types of Events

Type Description Example
Command An explicit request from a user/system publish, cancel_order
Time Triggered by time passing after(30 days)
Condition Triggered when a condition becomes true when(stock == 0)
Internal Triggers an action without changing state / log_view

In code, events map to

Guards (if/else equivalent)

No if/else in state machines — use guarded parallel transitions instead.

Instead of if/else:

on publish:
  if price > 0:
    go to Active
  else:
    go to Rejected

Model as two guarded transitions:

Draft ──publish [price > 0]──────→ Active
Draft ──publish [price == 0]─────→ Rejected

Priority / else-equivalent:

Draft ──publish [price > 0 AND settings == 100]──→ Active     (1st)
Draft ──publish [else]───────────────────────────→ Rejected   (2nd / default)

Mental shift

Imperative (if/else) State machine
You write the flow You define the rules, the machine enforces them
Conditions buried in code Conditions visible on the diagram
Easy to add invalid paths Invalid transitions simply don't exist

Example — Product Lifecycle

[●] → Draft ──publish──→ Active ──archive──→ Archived
        │                   │
      delete              suspend
        ↓                   ↓
     Deleted            Suspended ──restore──→ Active

With guards and actions:

Draft ──publish [price > 0 AND split_settings total == 100]──→ Active
                / changelog.LogUpdate()

Active ──mark_sold_out──→ SoldOut
                        / notify_merchant()

Active ──archive──→ Archived

SoldOut ──restock──→ Active

When to Use